In the field of hydrate formation cementing, the method of developing the low hydration exothermic cement systems cannot effectively solve the problem of hydrate dissociation caused by the hydration heat release of cement. Therefore, we proposed a new approach to address this issue by employing cement additives that can effectively delay the dissociation of hydrate. In our previous work, we designed a novel hydrate dissociation inhibitor, PVCap/dmapma, however, its applicability with cement slurry remains unverified. In this study, we established a more realistic model of oilwell cement gel based on experimental data. Additionally, we investigated the potential effects of PVCap/dmapma on the microstructure and mechanical properties of cement gel through molecular simulations. The results suggest that PVCap/dmapma has no negative effect on the performance of cement slurry compared to Lecithin. By adding PVCap/dmapma to cement slurry, the problem of cementing in hydrate formations is expected to be solved.

Developing unconventional reservoirs through gas injection has become increasingly popular in recent years. Among the various injector gases, hydrocarbon gas is considered one of the most promising fluids for use in the EOR process. In this study, molecular dynamics simulations have been utilized to generate insights into the tight oil migration under six different hydrocarbon gas composition ratios. Simulation results indicate that the migration process of the oil-gas mixture occurs in stages, but the overall states of all systems remain relatively consistent. As the proportion of heavy components (ethane and propane) in the hydrocarbon gas increases, the threshold migration resistance of each system exhibits a pattern of initially decreasing and then increasing. The mechanism underlying the nonlinear evolutionary trend of migration resistance was clarified through analyzing dynamic interactions and interfacial tension characteristics. The essence lies in the fact that the hindrance effect caused by increasingly stronger oil/gas-pore interactions eventually outweighs the drag reduction effect induced by the gradual reduction of oil/gas-water interfacial tension. Based on migration characteristics and sensitivity factors, we propose that the optimal hydrocarbon gas composition ratio for methane/ethane/propane is in the range of 80/10/10 to 70/15/15. Overall, this study focuses on employing molecular dynamics simulations to analyze the oil-gas migration characteristics at the nanoscale, aiming to provide more detailed insights for microscopic analysis and theoretical support for tight oil development.

The decomposition of hydrates can cause serious sand production and collapse problems, hindering the long-term effective production of hydrates. This study proposes a theory for framework reconstruction and reinforcement for deep-water hydrate layers based on grouting fracturing technology and chemical sand control principles. The setting liquid was injected via fracturing and grouting to form several cracks with a certain depth and width. The setting liquid remains in the fracture and solidifies to form a “reconstruction body.” Simultaneously, the setting liquid permeates and diffuses from the cracks to the surrounding hydrate layer, bonding with the sediment and forming a gradient solidification zone to achieve solidification and reinforcement of the hydrate layer. To achieve effective production of hydrates, the reconstruction body must consider internal reinforcement, sand control, and good permeability. The parameters of the reconstruction body were designed based on the geological characteristics of hydrate formation in a certain area. In order to effectively support the hydrate layer, the reconstruction body was designed with a 24 h compressive strength of at least 3.20 MPa and a long-term compressive strength of at least 17.70 MPa. To ensure that the permeability characteristics of the reconstructed body meet production needs, the permeability of the reconstructed body must be greater than that of the hydrate layer. The maximum concentrated pore size of the skeleton reconstruction body is designed to be 9 μm based on the particle characteristics of shale sand in hydrate reservoirs. This study provides a new approach to solving sand production and collapse.

Summary: The issues of short thickening time of geopolymer at higher temperature conditions are significant barriers to broader application. In this study, the effects of raw material proportions and additives (activators, retarders, and fluid loss agents) on the performance of metakaolin (MK)-fly ash (FA)-based geopolymer under conditions of 70°C were investigated, and the effect mechanism of retarders was analyzed. The results indicate that when sodium silicate is combined with sodium hydroxide, the geopolymer exhibits high strength. Specifically, when the FA/MK ratio is 6:4 and the water/solid ratio is 0.7, the geopolymer exhibits high strength and favorable rheological properties. The addition of 0.9% barium chloride dihydrate (BaCl2·2H2O), 4% zinc sulfate heptahydrate (ZnSO4·7H2O), 10% ethylene glycol (EG), or 10% ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) significantly increases the setting time, but this adversely affects the strength. This occurs primarily due to the products formed from the reaction between the retarder components and water glass or mineral components, which cover the surface of the raw materials and reduce the reaction rate. When utilizing a combined dosage of 0.9% barium chloride dihydrate (BaCl2·2H2O) and zinc sulfate heptahydrate (ZnSO4·7H2O) as a retarder, the thickening time of the geopolymer significantly increases. Furthermore, the addition of 0.5% carboxymethylcellulose sodium (CMC-Na) effectively controls water loss, with the initial setting time exceeding 45 minutes and strength of up to 8 MPa, demonstrating satisfactory settlement stability, but it adversely affects rheological properties.